Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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(a) TITLE OF THE INVENTION
TRUCK TRAFFIC MONITORING AND WARNING SYSTEMS AND
VEHICLE RAMP ADVISORY SYSTEM
(b) TECHNICAL FIELD TO WHICH THE INVENTION RELATES
This invention relates to traffic monitoring systems for monitoring commercial
vehicles.
(c) BACKGROUND ART
Many kinds of systems have been disclosed which monitor and/or control
traffic.
Typically, each highway department had a command centre that received and
integrated
a plurality of signals which were transmitted by monitoring systems located
along the
highway. Although different kinds of monitoring systems were used, the most
prevalent
system employed a roadway metal detector. In such system, a wire loop was
embedded
in the roadway and its terminals were connected to detection circuitry that
measured the
inductance changes in the wire loop. Because the inductance in the wire loop
was
perturbed by a motor vehicle (which included a quantity of ferromagnetic
material)
passing over it, the detection circuitry detected when a motor vehicle was
over the wire
loop. Based on this perturbation, the detection circuity created a binary
signal, called
a "loop relay signal", which was transmitted to the command centre of the
highway
department. The command centre gathered the respective loop relay signals and
from
these made a determination as to the likelihood of congestion. The use of wire
loops
was, however, disadvantageous for several reasons.
First, a wire loop system did not detect a motor vehicle unless the motor
vehicle
included a sufficient ferromagnetic material to create a noticeable
perturbation in the
inductance in the wire loop. Because the trend now is to fabricate motor
vehicles with
non-ferromagnetic alloys, plastics and composite materials, wire loop systems
will
increasingly fail to detect the presence of motor vehicles. It is already well
known that
wire loops often overlook small vehicles. Another disadvantage of wire loop
systems
was that they were expensive to install and maintain. Installation and repair
required that
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a lane be closed, that the roadway be cut and that the cut be sealed. Often
too, harsh
weather precluded this operation for several months.
Other, but non-invasive, systems have been suggested. US Patent 5,060,206,
patented October 22, 1991 by F. C. de Metz Sr., entitled "Marine Acoustic
Aerobuoy
and Method of Operation", provided a marine acoustic detector for use in
identifying a
characteristic airborne sound pressure field generated by a propeller-driven
aircraft. The
detector included a surface-buoyed resonator chamber which was tuned to the
narrow
frequency band of the airborne sound pressure field and which had a
dimensioned
opening formed into a first endplate of the chamber for admitting the airborne
sound
pressure field. Mounted within the resonator chamber was a transducer circuit
comprising a microphone and a preamplifier. The microphone functioned to
detect the
resonating sound pressure field within the chamber and to convert the
resonating sound
waves into an electrical signal. The pre-amplifier functioned to amplify the
electrical
signal for transmission via a cable to an underwater or surface marine vehicle
to undergo
signal processing. The sound amplification properties of the resonator air
chamber were
exploited in the passive detection of propeller-driven aircraft at airborne
ranges exceeding
those ranges of visual or sonar detection to provide 44 dB of received sound
amplification at common aircraft frequencies below 100 Hz. However, this
patent used
only a single electro-acoustic transducer for receiving acoustic signals
within a detection
zone, and did not teach spatial discrimination circuitry for representing
acoustic energy
emanating from a detection zone.
US Patent No. 3,445,637, patented May 20, 1969 by J. M. Auer, Jr., entitled
"Apparatus for Measuring Traffic Density" provided apparatus for measuring
traffic
density in which a sonic detector produced a discrete signal which was
inversely
proportional only to vehicle speed for each passing vehicle. A meter, which
was
responsive to the discrete signals, produced a measurement representative of
traffic
density. However, this patent used only a single electro-acoustic transducer
for receiving
acoustic signals within a detection zone, and did not teach spatial
discrimination circuitry
for representing acoustic energy emanating from a detection zone.
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US Patent No. 3,047,838, patented July 31, 1962 by G. D. Hendricks, entitled
"Traffic Cycle Length Selector" provided a traffic cycle length selector which
automatically related the duration of a traffic signal cycle to the volume of
traffic in the
direction of heavier traffic along a thoroughfare. The Hendricks system did
not teach
the use of electro-acoustic transducers, but instead used pressure-sensitive
detectors.
While Hendricks employed plural, non-electro-acoustic transducers, the traffic
cycle
length selector system did not include spatial discrimination circuitry.
Hendricks merely
described the use of the output of several spatially discriminate detectors to
generate a
spatially indiscriminate signal.
There are, in addition, many other patents which are directed to systems which
monitor and/or control traffic. Amongst them are the following US Patents.
3,275,984 9/1966 Barker
3,544,958 12/1970 Carey et al.
3,680,043 7/1972 Angeloni
3,788,201 1/1974 Abell
3,835,945 9/1974 Yamanaka et al.
3,920,967 11/1975 Martin et al.
3,927,389 12/1975 Neeloff
3,983,531 9/1976 Corrigan
4,049,069 9/1977 Tamamura et al.
4,250,483 2/1981 Rubner
4,251,797 2/1981 Bragas et al.
4,284,971 8/1981 Lowry et al.
4,560,016 12/1985 Ibanez et al.
4,591,823 5/1986 Horvat
4,727,371 2/1988 Wulkowicz
4,750,129 611988 Hengstmengel
et al.
4,793,429 12/1988 Bratton et al.
4,806,931 2/1989 Nelson
5,008,666 4/1991 Gebert et al.
5,109,224 4/1992 Lundberg
5,146,219 9/1992 Zechnall
5,173,672 12/ 1992 Heine
5,231,393 7/1993 Strickland
5,315,295 5/1994 Fujii
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Specifically, some of these patents simply operated regular traffic signals or
warning signs. US Patent No. 4,908,616 disclosed a simple system deployed at a
traffic
signal controlled intersection. A warning device positioned in the approach to
the
intersection at a "reaction point" gave an indication to a driver as to
whether or not the
driver's vehicle was too close to the intersection to stop safely if the
traffic signal had
just changed. The system did not measure vehicle speed and cannot account for
differing
stopping distances for different classes of vehicle.
Systems which measure the speed of the vehicle included that disclosed in US
Patent No. 3,983,531, patented 9/1976, by Corrigan, which measured the time
taken for
a vehicle to pass between two loop detectors and operated a visual or audible
signal if
the vehicle was exceeding a set speed limit.
US Patent No. 3,544,958, patented 12/1970, by Carey, et al, disclosed a system
which measured the time taken for the vehicle to traverse the distance between
two light
beams and displayed the measured vehicle speed on a warning sign ahead of the
vehicle.
Conversely, US Patent No. 3,275,984, patented 9/1966, by Barker, disclosed a
system which detected when traffic was moving too slowly, thereby indicating
that a
highway was becoming congested, and activated a sign near a highway exit to
divert
traffic via the exit.
US Patent No. 4,591,823, patented 5/1986, by Horvat, disclosed a more
complicated system using radio transceivers which were located along the
roadway which
broadcast speed limit signals by transceivers carried by passing vehicles.
Signals
returned by the vehicle mounted transceivers enabled the roadside transceivers
to detect
speed violations and to report them to a central processor via modem or radio.
Traffic monitoring systems have also been disclosed which monitored various
parameters of the vehicle itself to enable the class of vehicle to be
determined. Thus,
US Patent No. 5,173,692, patented 12/1992, by Heine, disclosed a system for
controlling
access through a gate or entrance according to class of vehicle and which used
ultrasonic
detectors to detect vehicle profiles and compared them with established
profiles to
determine the class of vehicle.
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US Patent No. 3,927,389, patented 12/1975, by Neeloff, disclosed a system
which counted the number of axles on a vehicle to enable classification of the
vehicle and
the calculation of an appropriate tariff for use of a toll road.
Systems (known as WIM systems) were also known which used sensors to weigh
5 vehicles while they were in motion so as to detect, for example, overweight
commercial
vehicles. Examples of such systems are disclosed in US Patents Nos. 3,835,945,
patented 9/ 1974, by Yamanaka et al. ; 4,049,069, patented 9/ 1977, by
Tamamura et al. ;
4,560,016, patented 12/1985, by Ibanez et al.; and 4,793,429, patented
12/1988, by
Bratton et al.
US Patent number 5,008,666, patented 4/1991, by Gebert et al., disclosed
traffic
measurement equipment employing a pair of coaxial cables and a presence
detector for
providing measurements including vehicle count, vehicle length, vehicle time
of arrival,
vehicle speed, number of axles per vehicle, axle distance per vehicle, vehicle
gap,
headway and axle weights.
Lundberg, US Patent No. 4,109,224, disclosed a system which was concerned
with traffic conditions and the difficulty a driver had in assessing a safe
distance to the
vehicle ahead, especially when there was fog, ice or rain. Lundberg's system
had a
series of "cat's eyes" in the road surface which served as both signalling
devices and
sensors for detecting vehicle presence. The Lundberg sensors merely detected
vehicle
presence and the processor, using the distance between sensors, then computed
the speed
of the vehicle. Lundberg's system detected the speeds both of a lead vehicle
and a
following vehicle and used "pre-programmed rules" to determine whether or not
the
following vehicle was too close for its speed. If it was, the processor
lighted up the cat's
eyes in the road ahead to warn the driver of the following vehicle to slow
down. The
maximum safe speed was obtained from a table which listed several different
maximum
speeds for different weather conditions. Lundberg's system merely selected a
maximum
speed from the table regardless of the type of vehicle.
Hengstmengel, US Patent No. 4,750,129, was directed to the production of an
alarm signal on the basis of data obtained only from the speed of a vehicle
which actually
had overtaken a slower vehicle. Consequently, speed-limited signals were only
produced
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by signal display arrangements to warn the overtaking vehicle if there was a
real risk of
a collision.
The known systems did not, however, deal with the fact that a particular site
will
not be a hazard for one type of vehicle, for example an automobile, but will
be a hazard
for a truck. When commercial vehicles, especially large trucks, are involved
in
accidents, the results are often tragic. Statistics show that, although
commercial vehicles
are involved in a relatively small percentage of all motor vehicle accidents,
they are
involved in a higher percentage of fatal accidents than other vehicles.
Consequently,
they warrant special monitoring.
The invention previously made by the assignees of the present inventors
provided
an improved traffic monitoring system which was especially suited to
monitoring
commercial vehicles, namely in US Patent No. 5,617,086, patented April 1,
1997. That
invention was concerned with assessing whether or not the site constituted a
hazard for
a particular vehicle depending upon its size, weight, speed and the like. The
essence of
that invention was to use a variable parameter (vehicle speed) and a fixed
parameter
(vehicle weight) to provide information relative to the maximum speed at which
a hazard
may be safely negotiated based upon the site-specific data of that hazard.
That invention was therefore concerned with the fact that a hazard (e.g., a
particular curve, incline, controlled intersection, or the like) will not be a
hazard for one
type of vehicle, for example an automobile, travelling at a particular speed
but will be
a hazard for another type of vehicle, for example, a truck travelling at the
same speed.
Recognizing this, that system had sensors to measure the weight and, if
desired, one or
more other physical parameters of the vehicle, e.g., height, number of axles
or the like,
and a processor for storing data specific to the site, e.g., severity of an
incline,
curvature and chamber of a bend, or distance from the sensors to a controlled
intersection.
The processor used both the particular vehicle data and the site-specific data
to
compute a maximum speed for that particular vehicle safely to negotiate that
particular
hazard. In essence, therefore, the system used the weight and, if desired, one
or other
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more of the physical parameters of the vehicle to assess the forward momentum
of that
vehicle and to determine whether or not that vehicle can negotiate the hazard
safely.
Several different embodiments of that invention were taught. One embodiment
of that invention was directed to a traffic monitoring system which included a
set of
sensors which were disposed in a traffic lane approaching a hazard for
providing signals
indicative of the speed, and also indicative of at least the weight of a
vehicle traversing
the set of sensors. A processor had a memory for storing site-specific
dimensional data
related both to the hazard and to signals from the set of sensors. A traffic
signalling
device was associated with the traffic lane and was disposed downstream of the
set of
sensors, the traffic signalling device being controlled by the processor. The
processor
was responsive to the signals from the set of sensors for computing the actual
vehicle
speed. The processor also computed a maximum vehicle speed, which was derived
from
the site-specific dimensional data and from at least the weight of the
vehicle. The
computed maximum vehicle speed was thus the maximum speed for the vehicle
safely
to negotiate the hazard. The computed actual vehicle speed was compared with
the
computed maximum vehicle speed. The traffic signalling device was then
operated if the
computed actual vehicle speed exceeded the computed maximum safe vehicle
speed.
Another embodiment of that invention was a traffic monitoring system for use
in
association with a traffic-signal-controlled intersection having a set of
traffic signals and
a traffic signal controller. The system included a plurality of sensors which
were
disposed in a traffic lane upstream of the traffic-signal-controlled
intersection. The
plurality of sensors included a final sensor which was disposed a
predetermined distance
in advance of the intersection, a preceding sensor which was disposed a
predetermined
distance preceding a final sensor in the direction of traffic flow, and a
further sensor
which sensed weight of the vehicle for providing signals indicative of the
weight of the
vehicle. A processor was included which had a memory for storing site-specific
dimensional data including the predetermined distance. The processor was
responsive
to signals from the vehicle weight sensor, from the preceding sensor, and from
the final
sensor to compute a predicted vehicle speed at the final sensor. From the site-
specific
dimensional data the processor then determined whether or not the predicted
vehicle
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speed exceeded a computed maximum speed, at which speed the vehicle can safely
stop
at the intersection, should the traffic signals require it. If the vehicle
cannot safely stop
at the intersection, the processor transmitted a pre-emption signal to the
traffic signal
controller, thereby causing the traffic signal controller to switch, or to
maintain, the
traffic signal to afford right-of way through the intersection to that
vehicle.
Yet another embodiment of that invention provided a traffic monitoring system
for determining potential rollover of a vehicle, The sensor comprised a set of
sensor
arrays which were disposed in a traffic lane approaching a curve and a vehicle
height
sensor. The site-specific data included characteristics of the curve, e.g.,
camber and
curvature. The traffic signal device included a variable message sign
associated with the
traffic lane and which was disposed between the sensor arrays and the curve.
The
processor was responsive to the signals from the sensor array for computing,
as the
vehicle speed, a predicted speed at which the vehicle will be travelling on
arrival at the
curve, and derived the maximum speed for the particular vehicle to negotiate
the curve
safely on the basis of vehicle parameters, including weight and height. The
processor
compared the predicted speed with the maximum speed and operated the traffic
signal to
display a warning to the driver of the vehicle if the predicted speed exceeded
the
maximum speed. Such a system could be deployed, for example, at the beginning
of an
exit road from a highway, between the highway exit and a curved exit ramp, and
would
warn the driver of a tall vehicle travelling so quickly that there is a risk
of rollover as
it attempts to negotiate the curve. In such embodiment of that invention it
was necessary
also to measure the height of the vehicle as it approached a curve, since the
lateral
momentum of the vehicle in the curve can be predicted to determine the safe
speed at
which the vehicle can negotiate the curve without rollover. Thus, the system
of that
invention computed a safe maximum speed for a particular vehicle in dependence
upon,
among other things, the weight and height of the vehicle.
Thus, the following systems have now been provided:
A truck rollover advisory system, which is a system designed to reduce truck
rollover accidents which occur on highway exit ramps, in which in-road and off-
road
sensors determine individual truck speed, weight, height and type. From this
real time
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data/information, the probability of a particular truck rolling over is
computed by a
controller. A warning sign is automatically activated if an unsafe
configuration is
detected.
A downhill truck speed advisory system, which is a variable message sign to
advise individual trucks of a safe descent speed prior to beginning a long
downhill grade,
in which, as trucks approach the downhill grade, a controller computes
individual truck
weight and configuration and determines the maximum safe descent speed for
that
particular truck using FHWA (Federal Highway Administration) guidelines. A
variable
message sign displays the safe descent speed for individual trucks.
A runaway truck signal control system, which reduces the possibility of
disastrous
intersection accidents resulting from a runaway truck. As trucks proceed down
a slope,
the speed, weight and classification of each individual truck is determined.
If the truck
is travelling too fast to stop safely at the intersection downstream, a signal
will be
transmitted from a controller to the traffic signal lights. The lights will
either hold or
change to green until the oncoming truck travels through the intersection.
(d) DESCRIPTION OF THE INVENTION
While these systems have adequately addressed the problems of truck rollovers,
"runaway" trucks and downhill excess speed travel for trucks, some
improvements are
desirable. It would therefore be desirable to provide a system which made
maintenance
more efficient without unduly disrupting the traffic on the roadway. Thus, the
systems
of the prior art as discussed above, are expensive to install and maintain.
Moreover,
installation and repair require that a lane be closed, that the roadway be cut
and that the
cut be sealed. Often too, harsh weather can preclude this operation for
several months.
The present invention provides a first embodiment of a traffic monitoring and
warning system which includes a first set of sensors comprising a set of
electro-acoustic
sensors which are disposed above a traffic lane approaching a hazard for
producing
signals which are indicative of whether the vehicle is an automobile or a
truck and, if it
is a truck, to record and specify the configuration of the truck, a second set
of sensors
which are disposed in the traffic lane approaching the hazard for providing
signals which
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are indicative of the speed of a truck traversing the second set of sensors, a
processor
having a memory for storing site-specific dimensional data related both to the
hazard and
to signals which have been received from the sets of sensors, and a traffic
signalling
device which is associated with the traffic lane and which is disposed
downstream of the
5 second set of sensors, the traffic signalling device being controlled by the
processor, ~t
processor being responsive to the signals from the second sets of sensors for
computing
an actual speed of the truck and for computing a computed maximum speed of the
truck,
the computed maximum speed of the truck being derived from the site-specific
dimensional data and from at least the configuration of the truck, the
computed
10 maximum speed of the truck being a maximum speed for the truck of the
configuration
safely to negotiate the hazard, the processor comparing the computed actual
speed of the
truck with the computed maximum of safe speed for the truck, and the processor
then
automatically operating the traffic signalling device if the computed actual
speed of the
truck exceeds the computed maximum speed for the truck, and also discontinuing
operating the traffic signalling device if the computed actual speed of the
truck no longer
exceeds the computed maximum safe speed for the truck.
By a first variant of a second embodiment of the system of this invention, a
traffic
monitoring and warning system is provided comprising a first set of sensors
comprising
a set of electro-acoustic sensors which are disposed above a traffic lane
approaching a
curve for producing signals which are indicative of whether a vehicle is an
automobile
or a truck, and if it is a truck to specify the configuration of the truck, by
providing a
set of signals which are indicative of the configuration of the truck, a
second set of
sensors which are disposed in a traffic lane approaching a curve, the second
set of
sensors comprising a set of sensor arrays for providing signals which are
indicative of
the speed of the truck, a third set of sensors for providing signals which are
indicative
of the height of the truck, a processor having a memory for storing site-
specific
dimensional data comprising characteristics of the curve and signals which
have been
received from the sets of sensors, and a traffic signalling device which is
associated with
the traffic lane and which is disposed downstream of the sets of sensors, the
traffic
signalling device being controlled by the processor, the processor being
responsive to
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signals from the sets of sensors for computing an actual speed at which the
truck will be
travelling on arrival at the curve, and for deriving a computed maximum safe
speed for
the truck safely to negotiate the curve on the basis of the configuration of
the truck as
determined by the first set of sensors and on the basis of the height of the
truck as
determined by the truck height sensor, the processor comparing the computed
actual
speed of the truck with the computed maximum safe speed for the truck, and the
processor then automatically operating the traffic signalling device if the
computed actual
speed of the truck exceeds the computed maximum safe speed for the truck, to
display
a warning to a driver of the truck if the computed actual speed of the truck
exceeds the
computed maximum safe speed for the truck, and also discontinuing operating
the traffic
signalling device if the computed actual speed of the truck no longer exceeds
the
computed maximum safe speed for the truck.
By a second variant of the second embodiment of the system of this invention,
a
traffic monitoring and warning system and vehicle ramp advisory system is
provided
comprising a first set of sensors comprising a set of electro-acoustic sensors
which are
disposed above a traffic lane approaching a curve for producing signals which
are
indicative of whether a vehicle is an automobile or a truck, and if it is a
truck to specify
the configuration of the truck, by providing a set of signals which are
indicative of the
configuration of the truck, the first set of sensors also providing signals
which are
indicative of the speed of the truck, a processor having a memory for storing
site-specific
dimensional data comprising characteristics of the curve and signals which
have been
received from the first set of sensors, and a traffic signalling device which
is associated
with the traffic lane and which is disposed downstream of the first set of
sensors, the
traffic signalling device being controlled by the processor, the processor
being responsive
to signals from the first set of sensors for computing an actual speed at
which the truck
will be travelling on arrival at the curve, and for deriving a computed
maximum safe
speed for the truck safely to negotiate the curve on the basis of the
configuration of the
truck as determined by the first set of sensors, the processor comparing the
computed
actual speed of the truck with the computed maximum safe speed for the truck,
and the
processor then automatically operating the traffic signalling device if the
computed actual
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speed of the truck exceeds the computed maximum safe speed for the truck, to
display
a warning to a driver of the truck if the computed actual speed of the truck
exceeds the
computed maximum safe speed for the truck, and discontinuing operating of the
traffic
signalling device if the computed actual speed of the truck no longer exceeds
the
computed maximum safe speed for the truck.
By a third embodiment of the traffic monitoring and warning system of this
invention, the system comprises a first set of sensors comprising a set of
electro-acoustic
sensors which are disposed above a traffic lane approaching a traffic-signal-
controlled
intersection for producing signals which are indicative of whether a vehicle
is an
automobile or a truck, and, if it is a truck, to specify the configuration of
the truck, by
providing a set of signals which are indicative of the configuration of the
truck, a second
set of sensors comprising a plurality of sensors which are disposed in the
traffic lane
upstream of the traffic-signal-controlled intersection having a set of traffic
signals and a
traffic signal controller, the second set of sensors constituting the
plurality of sensors
comprising a final sensor which is disposed a predetermined distance from the
intersection, and a preceding sensor which is disposed a predetermined
distance preceding
the final sensor in the direction of traffic flow, the preceding sensor
providing signals
which are indicative of the speed of a truck traversing the set of sensors,
and a processor
for storing data including a predetermined distance, the processor being
responsive to
signals from the preceding sensor, to signals from the final sensor, and to
signals from
the electro-acoustic sensors, and to site-specific data, to compute an actual
speed of the
truck at the final sensor and to compute a maximum speed of the truck, and
then to
determine whether or not the computed actual speed of the truck exceeds a
maximum
speed of the truck from which the truck can safely stop at the intersection
should the
traffic signals require it, the processor transmitting a pre-emption signal to
the traffic
signal controller causing the traffic signal controller to switch, or to
maintain, the traffic
signal to afford right of way through the intersection to the truck in the
event that the
computed actual speed of the truck exceeds the computed maximum safe speed for
the
truck.
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13
By a fourth embodiment of the system of this invention, a traffic monitoring
and
warning system is provided comprising a traffic-signal-controlled section
having a set of
traffic signals and a traffic signal controller, the traffic monitoring system
comprising a
first set of sensors comprising a set of electro-acoustic sensors which are
disposed above
a traffic lane for producing signals which are indicative of whether a vehicle
is an
automobile or a truck, and, if it is a truck, to specify the configuration of
the truck, by
providing a set of signals which are indicative of the configuration of the
truck, a second
set of sensors comprising a plurality of sensors which are disposed in a
traffic lane
upstream of the traffic-signal-controlled intersection, the second set of
sensors
constituting the plurality of sensors comprising a preceding sensor which is
disposed a
predetermined distance in advance of the intersection and a final sensor which
is disposed
downstream from the preceding sensor in the direction of traffic flow, for
providing
signals which are indicative of the speed of a vehicle, and a processor having
a memory
for storing site-specific dimensional data including the predetermined
distance, the
processor being responsive to the signals from the truck configuration sensor,
from the
preceding sensor and from the final sensor to compute predicted actual speed
of the truck
at the final sensor, and for computing a maximum safe speed for the truck and
being
responsive to signals from the site-specific dimensional data to determine
whether or not
the predicted speed of the truck exceeds the computed maximum safe speed of
the truck
at which speed the truck can safely stop at the intersection curve, the
processor then
transmitting a pre-emption signal to the traffic signal controller, thereby
causing the
traffic signal controller to switch the traffic signal, or to maintain the
traffic signal, to
afford right of way through the intersection to the truck.
By a fifth embodiment of the traffic monitoring and warning system of this
invention, the system comprises a first set of sensors comprising a set of
electro-acoustic
sensors which are disposed above a traffic lane approaching a downgrade for
producing
signals which are indicative of whether a vehicle is an automobile or a truck,
and if it
is a truck, to indicate the configuration of the truck, for providing a set of
signals which
are indicative of the configuration of the truck, a second set of sensors
which are spaced-
apart along a traffic lane approaching the downgrade, the second set of
sensors providing
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signals which are indicative of the speed of truck, a processor having a
memory for
storing site-specific dimensional data related both to the downgrade including
the length
and severity of the downgrade and to signals from the sets of sensors, and a
traffic
signalling device associated with the traffic lane and disposed downstream of
the sets of
sensors, the traffic signalling device comprising a message sign, the message
sign being
controlled by the processor, the processor being responsive to the signals
from the sets
of sensors for computing a computed actual speed of the truck and for
computing a
computed maximum safe speed for the truck which is derived from the site-
specific
dimensional data and from at least the configuration of the truck, the
computed maximum
speed of the truck being a maximum safe speed for the truck safely to descend
the
downgrade, the processor, by comparing the computed actual speed of the truck
with the
computed maximum safe speed for the truck, only operating the message sign if
the
computed actual speed of the truck exceeds the computed maximum safe speed for
the
truck by transmitting a control signal to the message sign, thereby causing
the message
sign to display the maximum speed for a period of time during which the sign
is visible
to a driver of the truck.
By two variants of the system of this aspect of the invention, a signal for
discontinuing operating the traffic signalling device is based on a timer
which is
responsive to natural deceleration of the speed of the truck upon the driver
of the truck
acting on a warning provided by the traffic signalling device; or a signal for
terminating
display of the warning provided by the traffic signalling device comprises a
downstream
set of truck presence detectors and truck speed sensors, the downstream at
truck presence
detectors and truck speed sensors being situated downstream of the message
sign, the
downstream set of truck presence detectors being connected to the processor,
the
processor being responsive to a signal from the downstream set of truck
presence
detectors and truck speed sensors. By one variation of these variants of this
aspect of
the invention, the downstream set of truck presence detectors comprises a set
of sensors
comprising a set of electro-acoustic sensors which are disposed above a
traffic lane
approaching a hazard for producing signals which are indicative of the speed
of a truck
traversing the set of sensors.
CA 02238127 1998-OS-15
By another variant of the system of this aspect of the invention, the traffic
monitoring system includes a weigh-in-motion scale for supplementing the set
of signals
which are indicative of the configuration of the truck with signals which are
indicative
of the actual weight of the truck.
5 By a variant of the third embodiment of the system of this invention, the
second
set of sensors comprises a set of electro-acoustic sensors which are disposed
above a
traffic lane approaching a curve for producing signals which are indicative of
whether
a vehicle is an automobile or a truck, and if it is a truck to specify the
configuration of
the truck, by providing a set of signals which are indicative of the
configuration of the
10 truck, the second set of sensors also providing signals which are
indicative of the speed
of the truck.
By a variant of this fifth and sixth embodiments of the invention, the traffic
monitoring system includes a third set of sensors which is disposed between
the first set
of sensors and the second set of sensors.
15 By yet a further variant of the embodiment of this invention, the traffic
monitoring system includes a first sub-system of the second set of sensors
which
comprises above-road electro-acoustic sensors and at least one of presence
sensors which
is either an inductive loop, or a sonic detector; axle detectors which are
either
piezoelectric, capacitance, or fibre optic detectors; and height detectors
which are either
a laser, or a lightbeam.
By a variant of the fifth and sixth embodiments of the system of this
invention,
each of the second and third sets of spaced-apart sensor sub-systems comprises
axle
detectors, which are either piezoelectric, capacitance or fibre optic.
By yet another variant of the fifth and sixth embodiments of the system of
this
invention, the preceding sensor comprises first and second sensor arrays which
are
spaced apart along the traffic lane, the processor being responsive to the
data and to
signals from the first and second sensors for computing the maximum safe speed
of the
truck and being responsive to the signals from the final sensor array for
determining the
actual speed of the truck at the final sensor.
CA 02238127 1998-OS-15
16
By still another variant of the fifth and sixth embodiments of the system of
this
invention, the second set of sensors comprises first, second and third sensor
arrays which
are spaced apart along a traffic lane upstream of a traffic-signal-controlled
intersection
having a set of traffic signals and a traffic signal controller, the set of
sensors each
S including sensors for providing signals in dependence upon at least one
physical
parameter of the truck which is different from the length of the truck and the
number and
configuration of axles of the truck, the processor storing site-specific date
including
distances between the first and second sensor arrays, and between the third
sensor array
and the intersection, and the processor being responsive to the site-specific
data and to
signals from the second sensor array for computing a maximum safe speed for
the truck,
and being responsive to signals from the third sensor array for computing
actual speed
of the truck at the third sensor, the processor comparing the speed at the
third sensor
array with the computed maximum safe speed for the truck and, if the speed at
the third
sensor array exceeds the computed maximum safe speed of the truck, then the
processor
transmits a signal to the traffic signal controller, thereby causing the
traffic signal
controller to switch, or to maintain, the traffic signal to afford right of
way through the
intersection to the truck.
By yet a further variant of the fifth and sixth embodiments of the system of
this
invention, the traffic monitoring system further includes a camera device
which is
actuatable in dependence upon a selected signal to capture an image of a truck
causing
the selected signal. By a variation thereof, the traffic monitoring system
further includes
a vehicle presence detector downstream of the camera device for generating a
signal,
when traversed by the truck, for deactivating the camera device.
By other variants of the embodiments of the systems of this invention and the
variants and variations thereof, the set of electro-acoustic sensors comprises
a first
electro-acoustic sensor for receiving a first acoustic signal which is
radiated from the
truck at a predetermined zone and for converting the first acoustic signal
into a first
electric signal that represents the first acoustic signal, a second electro-
acoustic sensor
for receiving a second acoustic signal which is radiated from the truck at the
predetermined zone and for converting the second acoustic signal into a second
electric
CA 02238127 1998-OS-15
17
signal that represents the second acoustic signal, spatial discrimination
circuitry for
creating a third electric signal which is based on both the first electric
signal and on the
second electric signal, that substantially represents the acoustic energy
emanating from
the predetermined zone, frequency discrimination circuitry for creating a
fourth signal
which is based on the third signal, and interface circuitry for creating an
output signal
which is based on the fourth signal such that the output signal is asserted
when the truck
is within the predetermined detection zone and whereby the output signal is
retracted
when the truck is not within the predetermined detection zone. By one
variation thereof,
the frequency discrimination circuitry comprises a bandpass filter. By another
variation
thereof, the frequency discrimination circuitry comprises a bandpass filter
with a lower
passband edge substantially close to 4KHZ and an upper passband edge
substantially close
to 6KHz.
By still other variants of the embodiments of the systems of this invention
and the
variants and variations thereof, the electro-acoustic sensors comprise a
plurality of
electro-acoustic sensors which are trained on a predetermined zone, a bandpass
filter for
processing electrical signals from the plurality of electro-acoustic sensors,
a correlator
having at least two inputs and an output for correlating filtered versions of
the electrical
signals originating from at least two of the plurality of electro-acoustic
sensors, an
integrator for integrating the output of the correlator means over time, and a
comparator
for indicating detection of the truck when the integrated output exceeds a
predetermined
threshold. By one variation thereof, the system further includes a plurality
of analog-to-
digital convertors for converting the electrical signals to digital
representations prior to
the processing thereof. By another variation thereof, the integrator and the
comparator
are each microprocessor-based programs. By yet another variation thereof, the
plurality
of electro-acoustic sensors comprises two vertical and two horizontal multiple-
microphone elements, and the correlator means has one of the at least two
inputs
receiving a sum of the two multiple-microphone vertical elements, and the
other of the
at least two inputs receiving a sum of the two horizontal multiple-microphone
elements.
By another embodiment of this invention, a first embodiment of a method is
provided for automatically controlling the operation of a traffic signalling
device
CA 02238127 1998-OS-15
18
associated with a hazard by analyzing data from any of the systems described
above,
comprising the steps of: downloading a set of records of parameters of the
specific truck
and associated speeds derived from a set of sensors which are disposed
upstream of the
hazard into a processor, downloading a set of records for corresponding
parameters of
the specific truck and speeds derived from a set of sensors which are disposed
downstream of the hazard into the processor, matching records, by the
processor, of the
specific truck from both sets of records, computing, by the processor, from
the records,
an actual speed of the specific truck and a computed maximum safe speed for
the truck,
comparing, by the processor, an actual speed of the truck the computer
maximises safe
speed for the truck, automatically operating, by the processor, the traffic
signalling
device if the computed actual speed of the truck exceeds the computed maximum
safe
speed of the truck, to display a warning to a driver of the truck when the
computed
actual speed of the truck exceeds the computed maximum speed of the truck, and
discontinuing, by the processor, operating the traffic signalling device if
the computed
actual speed of the truck no longer exceeds the computed maximum safe speed
for the
truck.
By another embodiment of this invention, a second embodiment of a method is
provided for automatically controlling the operation of a traffic signalling
device
associated with a curve by analyzing data from any of the systems as described
above,
comprising the steps of downloading a set of records of parameters of the
specific truck,
including the height of the specific truck, and associated speeds derived from
a at least
two sets of sensors which are disposed upstream of the hazard into a
processor, matching
records, by the processor, of the specific truck from both sets of records,
computing, by
the processor, from the records, an actual speed of the specific truck and a
computed
maximum safe threshold speed for the truck from rollover threshold data which
has been
downloaded from the processor, calculating, by the processor, an anticipated
speed of
the truck at the point of curvature of the curve, automatically operating, by
the
processor, the traffic signalling device if the computed actual speed of the
truck exceeds
the computed maximum safe threshold speed of the truck, to display a warning
to a
driver of the truck when the computed actual speed of the truck exceeds the
computed
CA 02238127 1998-OS-15
19
maximum threshold speed of the truck, and discontinuing, by the processor,
operating
the traffic signalling device if the computed actual speed of the truck no
longer exceeds
the computed maximum safe speed for the truck.
By yet another embodiment of this invention, a third embodiment of a method is
provided for automatically controlling the operation of a traffic signalling
device at an
intersection by analyzing data from any of the systems as described above,
comprising
the steps of downloading a set of records of parameters of the specific truck
and
associated speeds derived from at least two sets of sensors which are disposed
upstream
of the hazard into a processor, matching records, by the processor, of the
specific truck
from both sets of records, computing, by the processor, from the records, an
actual
speed of the specific truck and a computed maximum stopping distance for the
truck from
stopping threshold data which has been downloaded into the processor,
downloading, into
the computer, the actual speed of the truck at a premeasured distance upstream
from the
traffic signalling device, determining, by the processor, whether the truck
will be able
to stop before the traffic signalling device, and from the determination,
sending, by the
processor, a signal to the traffic signalling device to pre-empt the traffic
signalling
device.
By a variation of these embodiments of methods of this invention, the method
includes the step of downloading a set of records of the actual weight of the
truck. By
another variation thereof, the discontinuing step is carried out by a signal
which is based
on a timer which is responsive to natural deceleration of the truck if a
driver of the truck
acts on the warning which was provided by the traffic signalling device,
thereby to
restore a default message to the traffic signalling devices. By yet another
variation
thereof, the discontinuing step is carried out by a signal which is based on
an actual
measured speed of the truck at the point of curvature of the curve, thereby to
restore a
default message to the traffic signalling device.
By a variation of the third embodiment of the method of this invention, the
method includes the step of addressing a video system to record truck passage
at the
traffic signalling device.
CA 02238127 1998-OS-15
By another aspect of this invention, a further method is provided for
detecting and
signalling the presence of a truck in a predetermined zone, the method
comprising the
steps of receiving, with a first electro-acoustic sensor, a first acoustic
signal which is
radiated from a motor vehicle and converting the first acoustic signal into a
first electric
5 signal that represents the first acoustic signal, receiving, with a second
electro-acoustic
sensor, a second acoustic signal which is radiated from the motor vehicle and
converting
the second acoustic signal into a second electric signal that represents the
second acoustic
signal, creating, with spatial discrimination circuitry, a third electric
signal, which is
based on the sum of the first electric signal and the second electric signal
such that the
10 third signal is indicative of the acoustic energy emanating from the
detection zone,
creating, with interface circuitry, a binary loop relay signal which is based
on the third
electric signal such that the loop relay signal is asserted when the motor
vehicle is within
the detection zone and such that the loop relay signal is retracted when the
motor vehicle
truck is not within the detection zone, and comparing the third electric
signal to electrical
15 signals from known trucks to determine whether the motor vehicle is a
truck, and to
compute the speed of the truck, and to compute and specify the configuration
of the
truck, including length, number of axles, spacing of axles and height.
By yet a further embodiment of this invention, a still further method is
provided
for detecting trucks moving through a predetermined zone, comprising the steps
of
20 training a plurality of electro-acoustic sensors on the predetermined zone,
filtering
electrical signals from the plurality electro-acoustic sensors, correlating at
least two of
the filtered electrical signals with one another, integrating the results of
correlation in the
immediately-preceding step over time, comparing the integrated result of t~e
immediately-preceding step to a predetermined threshold and indicating
detection of~ a
motor vehicle when the threshold is exceeded by the integrated result, and
comparing the
third electric signal to electrical signals from known trucks to determine
whether the
motor vehicle is a truck, and to compute the speed of the truck and to compute
and
specify the configuration of the truck, including length, number of axles,
spacing of axles
and height.
CA 02238127 1998-OS-15
21
By one variation thereof, the method further includes the step of converting
the
electrical signals to digital representations prior to the filtering. By
another variation
thereof, the steps of integrating and comparing are each computational
routines. By yet
another variation thereof, the plurality of electro-acoustic sensors comprises
two vertical
and two horizontal multiple-microphone elements, and the correlating step
continuously
correlates the sum of the two vertical multiple-microphone elements with sums
of the two
horizontal multiple-microphone elements.
(e) DESCRIPTION OF THE FIGURES
In the accompanying drawings:
FIG. 1 illustrates a first embodiment of the invention comprising a traffic
monitoring system installed upstream of a hazard for advising a driver of a
detected truck
of a safe speed for the truck;
FIG. 2 is a block schematic diagram of the system of FIG. 1;
FIG. 3 is a flowchart depicting the operation of a first processor unit of the
system of FIG. 2;
FIG. 4 is a flowchart depicting the operation of a second processor unit of
the
system of FIG. 2;
FIG. 5 is a flowchart depicting the subsequent processing of vehicle records
for
an optional embodiment of the system of FIG 3;
FIG. 6 illustrates first version of a second embodiment of the invention
comprising a truck monitoring system installed upstream of a curve, for
monitoring for
potential rollover of trucks negotiating the curve;
FIG. 7 is a simplified block schematic diagram of the system of FIG. 6;
FIGS. 8A and SB are flowcharts depicting the operation of the system of FIG.
6;
FIG. 9 illustrates second version of a second embodiment of the invention
comprising a truck monitoring system installed upstream of a curve of an off
ramp as a
vehicle ramp advisory system to help prevent rollover accidents and out of
control
vehicles on sharp curves of freeway off ramps;
FIG. 10 is a simplified block schematic diagram of the system of FIG. 9;
CA 02238127 1998-OS-15
22
FIGS. 11A and 11B are flowcharts depicting the operation of the system of
FIG. 8;
FIGS. 12 and 13 illustrate a third embodiment of the invention in the form of
a
traffic monitoring system installed upstream of a traffic-signal-controlled
intersection and
operable to pre-empt the traffic signals;
FIG. 14 is a simplified block schematic diagram of the system of FIGS. 12 and
13;
FIGS. 15A and 15B are flowcharts depicting operation of the system of FIGS. 12
and 13;
FIG. 16 is a side elevational view of the mounting of electro-acoustic sensor
array
sensors forming essential elements of the systems of embodiments of the
present
invention;
FIG. 17 is a drawing of an illustrative embodiment of an electro-acoustic
sensor
array constituting an essential element of the systems of the present
invention as it is used
to monitor the presence or absence of a truck in a predetermined detection
zone;
FIG. 18 is a drawing of an illustrative microphone array as can be used in the
illustrative embodiments of an electro-acoustic sensor array sensor
constituting an
essential element of the systems of embodiments of the present invention;
FIG. 19 is a block diagram of the internals of an illustrative detection
circuit as
shown in FIG. 17;
FIG. 20 is a detailed block diagram of a preferred embodiment of the electro-
acoustic sensor array sensor constituting an essential element of the systems
according
to embodiments of the present invention; and
FIG. 21 is a flow chart showing the operation of the controller block shown in
FIG.20.
(f) AT LEAST ONE MODE FOR CARRYING OUT THE INVENTION
(i) DYNAMIC DOWNHILL TRUCK SPEED WARNING SYSTEM
A generic aspect of the invention will now be described with reference to
FIGS.
1 through 5. This generic aspect comprises a warning system which is installed
at the
CA 02238127 1998-OS-15
23
approach to a hazard, whether it be a curve, an incline, a blind intersection,
a traffic-
signal controlled intersection, etc.
Referring to FIGS. 1 and 2, the hazard warning system comprises, at a first
sensor station, a truck classification system comprising a set of electro-
acoustic sensors
1711,(namely, 1711A, 1711B) for classifying trucks by means of signals in
dependence
upon the length of the truck and the number and arrangement of axles of the
truck. The
electro-acoustic sensors can determine whether the detected vehicle is a
truck, or is not
a truck, by an analysis of the sounds emanating from the detected vehicle. In
addition,
the length of the vehicle can be determined by the length of time between the
beginning
of the detection of the vehicle and the ceasing of detection of the vehicle in
its traversing
through the detection zone of a known length. Finally, the speed of the
vehicle can be
determined by the length of time for the vehicle to traverse the detection
zone of a known
length. The hazard warning system also comprises a first pair of sensor arrays
12,13 -
which may be of the type which are embedded in a roadway surface in the left-
hand and
right-hand traffic lanes, respectively. The sensor arrays 12,13 comprise
vehicle presence
detectors, and direct axle sensors which may comprise piezo-electric Class 1
sensors, or
inductive loop presence detectors. Each of these sensor arrays 12, 13 may be
used to
determine the speed of the detected vehicle by the length of time for the
detected vehicle
to traverse the detection zone of a known length. While these are preferred,
suitable
alternative sensors and detectors could be used, e.g., those disclosed in the
patents cited
in the introduction of this specification.
On-scale detectors (not shown) may be incorporated in each lane adjacent to
each
of the sensor arrays 12,13. The on-scale detectors ensure that the trucks
passing over
the in-road sensor arrays 12,13 are fully within the active sensor zone of the
sensor and
are not straddling a lane. The on-scale detectors effectively eliminate the
possibility that
a truck which was improperly classified will receive a message recommending a
speed
that is higher than is safe for that particular truck.
The electro-acoustic sensors 1711 also assure that errors incurred by a truck
straddling a lane do not affect the safe speed calculation. Therefore, such on-
scale
CA 02238127 1998-OS-15
24
detectors and/or such electro-acoustic sensors are important features of the
downhill
speed warning system of this embodiment of the present invention.
A short distance downstream from the sensor arrays 1711A, 1711B, 12, 13, two
traffic signal devices, in the form of electronic, variable message signs
14,15, are
positioned adjacent respective left-hand and right-hand traffic lanes. The
sensor arrays
1711A, 1711B ,12,13 and the electronic message signs 14,15 are connected to a
first
programmable roadside controller 16, which is conveniently located nearby. The
programmable roadside controller 16 comprises a microcomputer which is
equipped with
interfaces for conditioning signals from the sensors, and an interface for
transmitting a
control signal to the respective message sign 14, 15 for the lane in which the
vehicle is
travelling. The microcomputer is preprogrammed with hazard site-specific
software and
data, i.e., specifically related to the location of the sensors 1711A,1711B,
12, 13 and the
characteristics hazard, and truck classification data. It processes the
signals from the
sensor arrays and determines, for each truck, information including, but not
limited to,
number of axles on the truck, distance between axles, bumper-to-bumper vehicle
length,
vehicle speed and lane of travel of the truck. From the data derived from the
sensors
1711A, 1711B, it then determines truck class, i.e., based upon number of axles
and their
spacings. Using the hazard site-specific information and the truck
information, the
microcomputer computes an appropriate safe speed based on, inter alia, the
class of the
truck, and transmits a corresponding signal to the appropriate message sign
14,15 causing
it to display the safe speed while the truck passes through the region in
which the sign
can be viewed by the driver of the truck. The duration of the message is based
upon
hazard site-specific geometrics and varies from site to site.
The microcomputer creates a truck record and stores it in memory, with the
recommended safe speed, for subsequent analysis.
If the system cannot classify the truck accurately, e.g., when a truck misses
some
of the sensors by changing lanes, the system will not display a recommended
speed. In
such case, the variable message sign will display a default message, e.g.,
"Drive Safely".
The default message is user-programmable, allowing alternative messages to be
substituted.
CA 02238127 1998-OS-15
Downstream of the electronic message signs 14,15 is a second set of sensors
1711,(namely, 1711C, 1711D,) and sensor arrays 17,18, which are the same as
the first
set of sensors 1711 (namely, 1711A, 1711B) and sensor arrays 12,13, and so
need not
be described further.
5 These second set of sensor arrays 1711(namely, 1711C, 1711D), 17, 18, are
provided in conjunction with respective lanes of the roadway approximately one
kilometre (0.6 mile) beyond the variable message signs 14,15. These second set
of
sensor arrays 1711( namely, 1711C,1711D), 17, 18, are coupled to a secondary
roadside
controller 19 to form a secondary sub-system. This secondary sub-system
collects the
10 same information as the primary sub-system, but it is used only for
monitoring the
effectiveness of the primary system.
As seen in FIG 2, the roadside controllers 16 and 19 are equipped with modems
20,21, respectively, enabling remote retrieval of their truck record data, via
a telephone
system, by a central computer 23 in a central operations building (not seen).
15 Programmable controller 16 includes an AC or DC power line 16A, which is
connected
to an UPS 16B and to a power source 16C. Programmable controller 16 also
includes
a monitor 16D and a keyboard 16E. Likewise, programmable controller 19
includes an
AC or DC power line 19A, which is connected to an UPS 19B and to a power
source
19C. Programmable controller 19 also includes a monitor 19D and a keyboard
19E.
20 Each controller 16, 19 may also have an interface or communications port
enabling the
truck records to be retrieved by, for example, a laptop computer. The system
may also
allow system operators to have full control over the primary sub-system 1711
(namely,
1711C, 1711D), 12, 13, 16, including a disabling function and the ability to
change the
message on the variable message signs. The remote computer also has data
analysis
25 software providing the ability to take two data files (one from the primary
sub-system
and another from the secondary sub-system) and to perform an analysis on the
compliance of the truck operator to the variable sign messages. Specific truck
records
from the two sub-systems can be matched, and reports can be generated on the
effectiveness of the speed warning system.
CA 02238127 1998-OS-15
26
The sequence of operations as a vehicle (namely, a truck) is processed by the
system is depicted in the flowcharts shown in Figures 3 and 4, and subsequent
analysis
in the flowchart of Figure 5. For convenience of description, it will be
assumed that the
vehicle is in the left-hand lane. It will be appreciated, however, that the
same process
would apply to a vehicle in the other lane. Referring first to Figure 3, which
depicts
operation of the primary roadside controller 16, when a vehicle passes under
vehicle
electro-acoustic sensors 1711A and over sensor arrays 12, the microcomputer
receives
a vehicle detection signal, step 3.1, and confirms, in decision step 3.2,
whether or not
the vehicle has been detected accurately. If it has not, step 3.3 records an
error. If the
vehicle has been detected accurately, and if no weigh-in-motion scale is
present, a typical
weight and configuration of the truck is assumed. The microcomputer creates a
truck
record containing this information, namely, axle spacings and number of axles,
length
and electro-acoustic data, together with the time and date at step 3.4. If a
weigh-in-
motion scale (WIM) is present at 3.31, the actual weight, as well as other
information,
namely, axle spacings and number of axles, length and electro-acoustic data,
together
with the time and date is recorded at step 3.32. Comparing the information
with truck
classifications stored in its memory, the microcomputer determines in step 3.5
whether
or not the vehicle is a truck. If it is not, no further action is taken, as
indicated by step
3.6. If it is a truck, step 3.7 conducts a speed comparison of the actual
speed with a
nominal recommended speed, and accesses a truck class specific speed table to
determine, for that truck class, a recommended safe speed for that truck
safely to
negotiate the hazard. In step 3.8, the microcomputer conveys a corresponding
signal to
variable message sign 14 which displays a "WARNING" message. The truck driver
is
expected to gear down and to take due action as regard to nature of the
hazard. Once
the truck passes the variable message sign 14, steps 3.9 and 3.10 restore the
variable
message sign to the default message. The default restoration signal may be
generated
when the truck triggers a subsequent termination sensor (not shown), or a
timer "times-
out" after a suitable time-out interval. Step 3.11 stores the truck record,
including the
recommended speed, in memory for subsequent retrieval, as indicated by step
3.12, using
CA 02238127 1998-OS-15
27
a floppy disc, via modem, a laptop or any other suitable means of transferring
the data
to the central computer for subsequent analysis.
After passing through part of the distance to the hazard, the truck passes the
region of the second set of sensor arrays, e.g., sensor 1711C, and sensor
arrays 17, and
the secondary roadside controller 19 receives a vehicle presence signal, as
indicated in
step 4.1 in Figure 4. The secondary programmable roadside controller performs
an
abridged set of the operations which were carried out by the primary roadside
controller
16. Thus, following receipt of the vehicle presence signal in step 4.1, it
determines in
step 4.2 whether or not the truck was accurately detected. If it was not, step
4.3 records
an error. If it was, in step 4.4, the signals from the sensor 1711C and from
the sensor
arrays 17 are processed to produce a secondary truck classification record,
e.g., axle
spacings, number of axles, weight, if available, length, speed and other
electric-acoustic
data, together with the time and date. Using this information, and truck
classification
data which are stored in memory, step 4.5 determines whether or not the
vehicle is a
truck. If it is not, no further action is taken, as indicated by step 4.6. If
it is a truck,
step 4.7 stores the vehicle record in memory. As in the case of the primary
controller
16, the truck records can be downloaded to a floppy disc, a laptop computer
which is
connected via a suitable port, or via a modem to the central computer, for
subsequent
analysis to determine the effectiveness of the system.
Figure 5, shows an optional flowchart for the analysis by the central
computer,
but only if a weigh-in-motion scale (WIM) is present. If such weigh-in-motion
scale
(WIM) is present, truck records are downloaded in step 5.1 from both
programmable
controllers 16 and 19 and are compared in step 5.2 to match each primary truck
record
from the primary controller 16 with a corresponding secondary truck record,
i.e. for the
same truck, from the secondary controller 19. The comparison is based on time,
number
of axles, axle spacings and length of truck. A file is then created containing
the primary
truck record number from the primary controller 16, the truck secondary record
number
from the secondary controller 19, date and time from the primary controller,
the speed
of the truck as measured by the primary controller, the recommended speed, and
the
speed of the truck as measured by the secondary controller. Displaying or
printing the
CA 02238127 1998-OS-15
28
matched records, as in step 5.3, enables a comparison to be made between the
speed of
the truck when it traversed the first set of sensor arrays 12, and sensor
1711A and its
speed when it traversed the second set of sensor arrays 17, and sensor 1711C.
Step 5.4
determines the percentage of trucks which decreased speed as advised.
The generic hazard truck speed warning system as described above, is not
intended to replace runaway truck ramps, but to complement the ramps and
potentially
decrease the probability of required use of these ramps.
(ii) ROLLOVER WARNING SYSTEM
A first variation of a second embodiment of the invention, the rollover
warning
system, for detecting potential rollover of a truck approaching a curve, will
now be
described with reference to FIGS 6 through 8B. Figure 6 shows the components
of a
traffic monitoring system deployed between an exit 60 of a highway 61 and a
curved
ramp 62 of the exit road 63. The system comprises a first set of above-road
electro-
acoustic sensor arrays 1711E and a first set of in-road sensor arrays 64, 65,
namely
station # 1 sensor array 64 and station # 2 sensor array 65, which are spaced
apart along
the left hand lane of the exit road upstream of the curve 62. The exit road
has two lanes
and a duplicate set of sensors 1711 (namely, 1711F), 64A, 65A, 66A, and a
traffic signal
device 68A are provided for the right hand lane. Since the operation is the
same for both
sets of sensors, only the set in the left hand lane will be described further.
Sensors 1711
(namely, 1711E) comprise electro-acoustic sensors which are similar to those
used in the
first embodiment. Sensor arrays 64, 65, which comprise vehicle presence
detectors and
axle sensors, are similar to those used in the first embodiment, and are
spaced
downstream from sensors 1711 (namely, 1711E). A height detector 67, 67A is
positioned alongside the left hand lane. The height detector 67 may comprise
any
suitable measuring device, e.g., a laser or other light beam measuring device.
A traffic
signal device, in the form of an electronic message sign 68, 68A, is disposed
downstream
from sensor arrays 65, 65A, and is associated with the respective left hand
traffic and
right hand traffic lanes, for example above it or adjacent to it.
Referring now to Figure 7, the station # 1 sensors (1711E), the station # 2
sensors
(64), the station # 3 sensors (65), the overheight detector 67 and the
electronic message
CA 02238127 1998-OS-15
29
sign 68 are connected to a roadside controller 69 which comprises the same
basic
components as the roadside controller of the first embodiment described above,
including
a microcomputer and a modem 70. The microcomputer contains software and data
for
processing the sensor signals to give vehicle class based on vehicle length,
number of
axles and axle spacings, and vehicle speed. The microcomputer is
preprogrammed, upon
installation, with data specific to the site, e.g., camber and radius of the
curve, and the
various distances between the sensor arrays and the curve. In use, the
processor uses the
site-specific data, and the truck-specific data derived from the sensor arrays
1711E, 64,
65, 67 to compute deceleration between the sensor arrays and predict the speed
at which
the truck will be travelling when it arrives at the curve 62. Taking into
account height
and class of the truck, and camber and radius of the curve, it determines a
maximum safe
speed at which that particular class of truck should attempt to negotiate the
curve. If the
predicted speed exceeds this maximum, implying a risk of rollover occurring,
the
processor activates the message sign to display a warning, e.g., SLOW DOWN! or
some other suitable message. The sign is directional and is viewed only by the
driver
of the passing truck. The threshold speed is programmable and can be input or
changed
by the system user.
The sequence of operations as a vehicle is processed by the system will now be
described with reference to FIGS. 8A and 8B. When the vehicle passes under
electro
acoustic sensors 1711E, the analysis of the sound determines whether the
vehicle is a
truck or is not a truck. When the vehicle passes over sensor arrays 64, 65 the
resulting
presence detection signal from the presence detector at sensor arrays 64, 65
is received
by the processor in step 8.1 and the processor determines, in step 8.2,
whether or not
a vehicle has been accurately detected. If it has not, step 8.3 records an
error. If the
vehicle has been detected accurately, and if no weigh-in-motion (WIM) scale is
present,
a typical weight and configuration of the truck is assumed. The microcomputer
creates
a truck record containing this information, namely, axle spacings and number
of axles,
length and electro-acoustic data, together with the time and date at step 8.4.
On the
other hand, if a weigh-in-motion (WIM) scale is present at 8.31, the actual
weight, as
well as other information, namely, axle spacings and number of axles, length
and electro-
CA 02238127 1998-OS-15
acoustic data, together with the time and date is recorded at step 8.32. The
micro
computer uses this information, together with the time and date, to create a
vehicle
record. In decision step 8.5, from the information at steps 8.4 or 8,32, the
micro
computer compares the measurements with a table of vehicle classes to
determine
5 whether or not the vehicle is of a class listed, specifically one of various
classes of truck.
If it is not, the processor takes no further action as indicated in step 8.6.
If decision step
8.5 determines that the vehicle is a truck, however, the processor determines
in steps 8.7
and 8.8 whether or not the truck was also accurately detected at sensor array
65. If not,
an error is recorded in step 8.9. If it is detected accurately, the processor
processes the
10 signals received from sensor 65 to compute, in step 8.10 the corresponding
measurements
as in step 8.4.
Station #2 may not be present in all systems, and, in such case, the system
would
then proceed from step 8.5 directly to step 8.14.
In step 8.14, the processor determines whether or not vehicle height is
greater
15 than a threshold value (e.g., eleven feet). If the vehicle height is
greater than the
threshold value, the processor proceeds to step 8.15 to identify it as a
particular class of
truck. If the height of the vehicle is less than the threshold value, step
8.16 identifies the
truck type. Having identified the truck type in step 8.15 or step 8.16, the
processor
proceeds to access its stored rollover threshold tables in step 8.17 to
determine a
20 threshold speed for that particular truck safely to negotiate the curve. In
step 8.18, the
measured speed at station ~ 1 is the speed of the truck when it arrives at the
beginning
of the curve 62. Step 8.19 compares the predicted speed with the rollover
threshold
speed. If it is lower, no action is taken, as indicated by step 8.20. If the
predicted speed
is higher than the rollover threshold speed, however, step 8.21 activates the
message sign
25 68 for the required period to warn the driver of the truck to slow down.
Step 8.22 represents the sequence of steps by the processor to process the
corresponding signals from sensor array 66 to ascertain the speed of the truck
and the
type of truck, and to create a secondary record. Subsequent transmission of
the truck
data derived from all three sensor arrays 64, 65, 66 to a central computer, or
retrieval
30 in one of the various alternatives outlined above, is represented by step
8.23.
CA 02238127 1998-OS-15
31
Sensor array 66 is optional and is for system evaluation purposes. It is
positioned
between the electronic message sign 68 and the curve 62 and is used to monitor
whether
or not the message is heeded, i.e., whether or not trucks are slowing down
when
instructed to do so by the message sign. The signals from its sensors are also
supplied
to the programmable controller 69. This sensor array 66 need only supply
information
to enable truck speed to be determined and so comprises a truck axle sensor
and a truck
presence detector which is activated when a truck enters its field. The
controller 69
processes the signals from sensor array 66 to produce a secondary truck
record. As
before, data from the controller 69 can be downloaded to a remote computer and
truck
records from the first and second sensor compared with the corresponding truck
record
from the third sensor to determine the speed of the truck before and after the
message
sign. This allows statistics to be accumulated showing the number of trucks
slowing
down when instructed to do so by the sign, thereby allowing evaluation of
system
effectiveness.
The system algorithm is site specific to accommodate certain site
characteristics.
The software can be compiled on any curve site with a known camber and radius.
The
data is stored on site in the programmable controller and is retrievable
either by a laptop
computer on site or remotely via modem communication. The controller also has
an
auto-calibration feature. If the system fails for any reason, an "alert"
signal is
transmitted to the host computer via modem, informing the system operators of
a system
malfunction.
The programmable controller allows the system operator to adjust maximum
allowable safe speeds, based on collected data on truck speeds at particular
locations.
For example, if the maximum safe speed is set at the posted speed limit, but
if the
majority of trucks are exceeding the posted speed limit at a particular
location, then the
variable message warning sign would be excessively activated, and the system
would lose
its effectiveness. Therefore, it is desirable to adjust speed threshold
parameters to
increase system effectiveness. The centre of gravity for each truck is
estimated from the
rollover threshold tables.
CA 02238127 1998-OS-15
32
As an option to the main classification and detection sensors, on-scale
detectors
may be incorporated into each lane to ensure that the trucks passing the
sensor arrays are
fully within the active zone of the system, and are not straddling a lane. The
on-scale
detectors effectively eliminate the possibility that a truck will receive a
message for a
S speed that is higher than is safe for that particular truck.
The electronic message sign conveniently is installed directly below a
traditional
information sign (e.g., a "danger ahead" sign with the image of a truck
rolling over)
which indicates the ramp advisory speed. The message sign is not a continuous
beacon
which flashes continuously. Rather, it is a sign which is activated only when
a truck is
exceeding the rollover threshold speed at a particular curve. A message for a
specific
truck is more effective, since the sign is an exception to regular signing and
not a
common background feature.
(iii) VEHICLE RAMP ADVISORY SYSTEM
A second variation of the second embodiment of the invention, the Vehicle Ramp
Advisory System, for detecting potential rollover of truck approaching a
curve, will now
be described with reference to FIGS 9 through 11B. This second variation of
the second
embodiment of the invention, namely the Vehicle Ramp Advisory System (VRAS) is
an
intelligent transportation system which helps prevent rollover accidents and
out-of-control
vehicles on sharp curves, e.g., freeway exit ramps. Figure 9 shows the
components of
a VRAS traffic monitoring system deployed between an exit 90 of a highway 91
and a
curved ramp 92 of the exit road 93. The system comprises a first set of above-
road
electro-acoustic sensor arrays 1711F which are directed at the left hand lane
of the exit
road upstream of the curve 92, as station # 1 sensors. Sensor arrays 1711F
comprise
electro-acoustic sensors which are similar to those used in the first
variation of the
second embodiment. A typical orientation thereof will be described hereinafter
in FIG.
16. The system also comprises a second set of above-road electro-acoustic
sensor arrays
17116 which are directed at the right hand lane of the exit road upstream of
the curve
92, as station # 2 sensors. Since the operation is the same for both sets of
sensors, only
the set in the left hand lane will be described further. A traffic signal
device, in the form
of an electronic message sign 98, is disposed downstream from electro-acoustic
sensor
CA 02238127 1998-OS-15
33
arrays 1711F, and is associated with the left hand traffic lane, for example,
above it or
at an elevated height adjacent to it. The exit road has two lanes and hence a
duplicate
set of a traffic signal device 98A is provided for the right hand lane
downstream from
electro-acoustic sensor arrays 1711 G.
As an optional feature, the system may also comprises a third set of above-
road
electro-acoustic sensor arrays 1711H which are directed at the left hand lane
of the exit
road downstream of the first set of above-road electro-acoustic sensor arrays
1711E, but
upstream of the traffic signal device 98E, as station # 3 sensors. Sensor
arrays 1711E
comprise electro-acoustic sensors which are similar to those used in the first
version of
the second embodiment. In this optional feature, the system may also comprises
a fourth
set of above-road electro-acoustic sensor arrays 1711I, which are directed at
the left hand
lane of the exit road downstream of the first set of above-road electro-
acoustic sensor
arrays 17116 but upstream of the traffic signal device 98F, as station # 4
sensors:
Sensor arrays 1711I comprise electro-acoustic sensors which are similar to
those used in
the first variation of the second embodiment.
Referring now to Figure 10, the station # 1 sensors (1711F), the station # 2
sensors (17116), the station # 3 sensors (1711H), the station # 4 sensors
(1711I) and the
electronic message signs 68, 68A are connected to a roadside controller 99,
99B, which
comprises the same basic components as the roadside controller of the first
variation of
the second embodiment described above. The roadside controller 99 includes a
microcomputer 99B, and a modem 70. The microcomputer 99B contains software and
data for processing the sensor signals to give vehicle class based on vehicle
length,
number of axles and axle spacings, and vehicle speed. The microcomputer 99B is
preprogrammed, upon installation, with site-specific data, e.g., camber and
radius of the
curve, and the various distances between the sensor arrays and the curve. In
use, the
processor uses the site-specific data, and the truck-specific data derived
from the electro-
acoustic sensor arrays 1711F, 17116, 1711H, 1711I, to compute deceleration
between
the sensor arrays and to predict the speed at which the truck will be
travelling when it
arrives at the curve 92. Taking into account height and class of the truck,
and camber
and radius of the curve, the processor determines a maximum safe speed at
which that
CA 02238127 1998-OS-15
34
particular class of truck should attempt to negotiate the curve. If the
predicted speed
exceeds this maximum, implying a risk of rollover occurring, the processor
activates the
message sign to display a warning, e.g., TRUCK REDUCE SPEED! or some other
suitable message. The sign is directional and is viewed only by the driver of
the passing
truck. The threshold speed is programmable and can be inputted or changed by
the
system user.
More specifically, in this embodiment of the invention, the VRAS uses above-
road electro-acoustic sensors, known by the trade-mark SmartSonicT"', to
detect vehicles
and classify them according to type. All information from the electro-acoustic
sensors
is processed in real time, just milli-seconds after the vehicle has passed
through the
detection zone. If the speed of the vehicle (as determined by the above-road
electro-
acoustic sensors) exceeds the posted advisory speed, and the vehicle is
classified as a
truck, a warning status is assigned to the vehicle. The warning status
produces a trigger
signal which activates the message sign. The sign is only activated for
vehicles which
IS are assigned a warning status and is specific to that particular vehicle.
Since the signs
are only activated for particular vehicles, they are more noticeable and are
more likely
to achieve the desired response of vehicle speed reduction.
The VRAS is meant to complement the existing static signing by providing a
warning and drawing the attention of a driver to the fact that the safe speed
has been
exceeded and that the vehicle should slow down to avoid a potential rollover
or accident
resulting from a loss of control. It should be recognized that the accuracy of
the system
is dependent on site conditions and traffic flow characteristics.
In one particular embodiment, the message signs are fibre optic message signs.
The station #1 sensors, station #2 sensors, station #3 sensors, station ~I4
sensors, and
electronic message signs are all interlocked by suitable cables disposed
within, e.g., a
'/z" conduit 97. Typically, the distance between station #1 sensors 1711F and
electronic
message sign 98F is 250 feet, and the distance between station #2 sensors 71 G
and
electronic message sign 98G is likewise 250 feet.
As will be further described with reference to Fig. 16, the above-road electro-
acoustic sensors are mounted on poles.
CA 02238127 1998-OS-15
A truck entering the system passes through the above-road electro-acoustic
sensor
detection zones. As noted above, the sensors are mounted on poles and are
aimed at
specific areas on the roadway through which the traffic will pass. Since two
lanes are
to be equipped at this site, sensors are installed on both shoulders. For each
lane, two
5 detection zones are used. The above-road electro-acoustic sensors provide
data which
is processed by the controller electronics to determine a inter alia vehicle
speed.
If a warning status is assigned by the system, the roadside message signs will
be
activated for that particular vehicle. The sign will remain on for a specified
period of
time, until the vehicle has passed the static sign. A single controller is
used to receive
10 and process information from all of the above-road electro-acoustic sensors
plus control
the operation of the message signs. The electronics are compact and therefore
easy to
mount on the same pole that is used to mount the sensors. In one embodiment of
this
invention, where Station # 1 and Station #2 sensors only are used, a timer
will shut off
the message sign based on the time the vehicle is detected and the vehicle
speed.
15 The fibre optics message sign is a highly visible roadside message sign to
provide
a real-time, eye-catching message to truck drivers. A simple single message
fibre optic
sign is used clearly to communicate to the driver. For example, the sign may
contain
the message:
TRUCK
20 REDUCE
SPEED
The illumination of the sign is controlled by electronics. When a warning
message is necessary, the system turns the sign on so that the targeted driver
sees the
message. The timing of the activation and duration of the sign is controlled
to give
25 optimum visibility and viewing time to the driver, while minimizing the
possibility of a
following driver viewing the sign in error.
The sign has a minimum of two different and adjustable intensities for day and
night light levels, ensuring good visibility. Sign characters would have a
minimum
height of 10" and are readable from a distance of at least 500 feet under all
lighting
30 conditions.
CA 02238127 1998-OS-15
36
The housing of the sign preferably is aluminum alloy with a minimum thickness
of 0.125". All exterior seams are preferably welded and made smooth. The
entire
housing is preferably made weatherproof. A rubber seal or other approved seal
material
would preferably be provided around the entire door to ensure a watertight
enclosure.
The sign message preferably consists of fibre optic bundles which are arranged
to form the required letters. Each bundle preferably consists of a minimum of
600
fibres, ground smooth and polished at the input and output ends for maximum
light
transmission. Spare bundles numbering at least 5 % of the total bundles are
connected
to each light source for future replacement of damaged bundles.
The light source for each bundle is from two 50 watt quartz halogen lamps with
at least an average 6000 hour rated life. A minimum of four bulbs preferably
is provided
for the entire sign. No more than 50 % of the illumination of each bundle
preferably
comes from a single bulb. In the event of the failure of a single bulb in a
pair, the
bundles continue to be illuminated at 50% of normal brightness. Alternating
bundles in
a sign face preferably are connected to different light sources, such that a
lamp failure
will affect only alternating pixels.
In another embodiment, where Station # 3 and Station # 4 sensors are used,
these
sensors, which determine deceleration and predict speed, can be used to turn
off the sign
based on that speed. In this embodiment, therefore, the operation of the
message signs
is controlled by the vehicle speed.
The controller electronics passes the real time vehicle information to a micro-
controller. All vehicle information is stored in the memory of the controller
and is
retrievable manually at the controller cabinet. Data which is collected by the
system
includes vehicle counts, vehicle speed, and vehicle length (according to the
three
classification groups). The microcontroller receives and processes vehicle
information
to make a decision on the sign operation. If required, the controller
activates and
deactivates the real time warnings provided for drivers at the appropriate
time.
The above-road electro-acoustic sensors are used to provide vehicle speed
information. The above-road electro-acoustic sensors are mounted on a pole at
a height
of approximately 20 feet just off the shoulder of the road. Each sensor is
directed at a
CA 02238127 1998-OS-15
37
particular area on the roadway. A bank of microphones in the sensor monitors
the
acoustic energy from the detection zone. The noise is filtered and analyzed to
determine
vehicle presence, type, and speed.
The system operates as a vehicle advisory system by collecting vehicle speed
and
classification information. The passage of vehicles is monitored in real time,
and
determines whether the maximum safe entrance speed for that particular vehicle
is
exceeded. The system triggers the roadside message sign only if a vehicle is
exceeding
the posted maximum speed.
Raw vehicle records will include the following data, namely, site
identification,
time and date of passage, lane number, vehicle sequence number, vehicle speed,
and
code for invalid measurement.
The sequence of events for a vehicle record and message generation is outlined
as follows:
1. Vehicle Data Collection:
The operation of the VRAS is triggered by a vehicle through the above-road
electro-acoustic sensors detection zone. When a vehicle passes through the
detection
zone, the system creates a new vehicle record to contain all of the
information obtained
for that vehicle. After passing through the detection zone, the controller
processes the
vehicle record to determine classification (length class) and speed.
2a. Warning Status Determination:
If the vehicle speed recorded during vehicle data collection is greater than
the
posted advisory speed, a warning status will be assigned specifically to that
vehicle.
2b. A second set of sensors determines deceleration and calculated predicted
speed.
3. Message sign activation:
As the vehicle continues along the roadway, the sign will be deactivated
according
to a timer or, according to Step 2a, if the predicted speed is now below the
posted
advisory speed. Thus, the message sign will only be activated when necessary.
The sequence of operations as a vehicle is processed by the system will now be
described with reference to FIGS. 11A and 11B. When the vehicle passes under
sensor
1711F, the analysis of the sound determines whether the vehicle is a truck or
is not a
CA 02238127 1998-OS-15
38
truck at step 1 1. l . The processor determines, in step 11.2, whether or not
a vehicle has
been accurately detected. If it has not, step 11.3 records an error. If the
vehicle has
been detected accurately, and if no weigh-in-motion (WIM) scale is present, a
typical
weight and configuration of the truck is assumed. The microcomputer creates a
truck
record containing this information, namely, axle spacings and number of axles,
length
and electro-acoustic data, together with the time and date at step 11.4. On
the other
hand, if a weigh-in-motion (WIM) scale is present at 11.31, the actual weight,
as well
as other information, namely, axle spacings and number of axles, length and
electro-
acoustic data, together with the time and date is recorded at step 11.32. It
uses this
information, together with the time and date, to create a vehicle record. In
decision step
8.5, from the information at steps 11.4 or 11.32, it compares the measurements
with a
table of vehicle classes to determine whether or not the vehicle is of a class
listed,
specifically one of various classes of truck. If it is not, the processor
takes no further
action as indicated in step 11.6. If decision step 8.5 determines that the
vehicle is a
truck, and that it was accurately detected, then, in step 11.14, the processor
determines
whether or not vehicle height is greater than a threshold value (e.g. eleven
feet). If the
vehicle height is greater than the threshold value, the processor proceeds to
step 8.15 to
identify it as a particular class of truck. If the height of the vehicle is
less than the
threshold value, steps 11.15 and 11.16 identify the truck class and type.
Having identified the truck type in step 8.15 or step 8.16, the processor
proceeds
to access its stored rollover threshold tables in step 11.17 to determine a
threshold speed
for that particular truck safely to negotiate the curve. In step 11.18, the
measured speed
at station # 1 is the speed of the truck when it arrives at the beginning of
the curve 92.
Step 11.19 compares the predicted speed with the rollover threshold speed. If
it is
lower, no action is taken, as indicated by step 11.20. If the predicted speed
is higher
than the rollover threshold speed, however, step 11.21 activates the message
sign 68 for
the required period to warn the driver of the truck to slow down.
If the system does not include station #3 sensors, a timer determines, from
the
speed of the vehicle and the time lapse, to deactivate the warning sign at
step 11.2b.
CA 02238127 1998-OS-15
39
If the system includes station #3 sensors, the vehicle is detected by the
sensors
at station #3 in step 11.22. The processor determines in step 11.23 whether or
not a
vehicle has been accurately detected. If it has not, step 11.34 records an
error. If the
vehicle has been detected accurately, the microcomputer creates a truck record
of the
speed together with the time and date at step 11.25. If such speed is lower
than the
rollover threshold speed, the timer sensed deactivation of the warning sign is
overridden,
but step 11.26 deactivates the message sign.
Step 11.27 represents the sequence of steps by the processor to process the
corresponding signals from electro-acoustic sensor arrays 1711 F and 1711 G to
ascertain
the speed of the truck and the type of truck, and to create a secondary
record.
Subsequent transmission of the truck data derived from all three sensor arrays
64, 65,
66 to a central computer, or retrieval in one of the various alternatives
outlined above,
is represented by step 11.23.
The controller 99 processes the signals from all the electro-acoustic sensor
arrays
to produce a secondary truck record. As before, data from the controller 99
can be
downloaded to a remote computer and truck records from the first and third
sensors
compared to determine the speed of the truck before and after the message
sign. This
allows statistics to be accumulated showing the number of trucks slowing down
when
instructed to do so by the sign, thereby allowing evaluation of system
effectiveness.
As in the first variation of the second embodiment of this invention, the
system
algorithm is site specific to accommodate certain site characteristics. The
software can
be compiled on any curve site with a known camber and radius. The data is
stored on
site in the programmable controller and is retrievable either by laptop
computer on site
or remotely via modem communication. The controller also has an auto-
calibration
feature. If the system fails for any reason, an alert signal is transmitted to
the host
computer via modem, informing the system operators of a system malfunction.
The programmable controller allows the system operator to adjust maximum
allowable safe speeds, based on collected data on truck speeds at particular
locations.
For example, if the maximum safe speed is set at the posted speed limit, but
if the
majority of trucks are exceeding the posted speed limit at a particular
location, then the
CA 02238127 1998-OS-15
variable message warning sign would be excessively activated, and the system
would lose
its effectiveness. Therefore, it is desirable to adjust speed threshold
parameters to
increase system effectiveness. The centre of gravity for each truck is
estimated from the
rollover threshold tables.
5 As an option to the main classification and detection sensors, on-scale
detectors
may be incorporated into each lane to ensure that the trucks passing the
sensor arrays are
fully within the active zone of the system, and are not straddling a lane. The
on-scale
detectors effectively eliminate the possibility that a truck will receive a
message for a
speed that is higher than is safe for that particular truck.
10 The electronic message sign , namely, TRUCK REDUCE SPEED !, conveniently
is installed directly below a traditional information sign (e.g., a "danger
ahead" sign with
the image of a truck rolling over) which indicates the vehicle ramp advisory
speed. The
message sign is not a continuous beacon which flashes continuously. Rather, it
is a sign
which is activated only when a truck is exceeding the rollover threshold speed
at a
15 particular curve. A message for a specific truck is more effective, since
the sign is an
exception to regular signing and not a common background feature.
(iv) TRAFFIC SIGNAL PRE-EMPTION SYSTEM
A third embodiment of the invention, the traffic signal pre-emption system,
specifically a traffic signal pre-emption system which monitors truck speed at
successive
20 points along a steep downgrade to determine when there is a "runaway" truck
and pre
empts traffic signals along the path of the runaway truck, will now be
described with
reference to FIGS. 12 through 15B.
The downhill speed warning system may be installed at the approach to a long,
steep downhill grade, perhaps at the summit of a mountain pass. The downhill
speed
25 warning system comprises a system of sensors and a programmable controller
for
classifying commercial vehicles, i.e. trucks, while they are in motion. Using
that
information and stored information which is specific to the downgrade, the
system
provides real-time safe descent speed calculations, and advises drivers of the
safe descent
speed by variable message signs, all before the truck begins to descend the
downgrade.
CA 02238127 1998-OS-15
41
This embodiment may also be used in conjunction with hazards at traffic-light-
controlled
intersections, or at blind intersections.
Figure 12 depicts a section through a steep downgrade 1202 with an
intersection
at the bottom. The intersection is controlled by traffic signals 1203 of
conventional
construction, i.e. the usual red, yellow and green lights controlled by a
traffic signal
controller 1402 (Figure 14). A truck 1201 is shown at the top of the
downgrade. As the
truck 1202 descends the downgrade, it will traverse a set of sensor arrays
shown in more
detail in Figure 13. As in the other embodiments, a set of sensor arrays is
provided for
each traffic lane. A camera 1204, whose purpose will be described hereinafter,
is also
provided, as is a utilities box 1205.
Each set of sensor arrays comprises sensor arrays, namely station # 1 sensors
comprising truck classification sensors in the form of electro-acoustic
sensors 1711J,
1711K, which are similar to those described previously, and sensor arrays
1305, 1305A,
1306 1306A, and 1307, 1307A, which are spaced apart in the road surface along
the
downgrade. Sensor arrays 1305, 1305A, 1306, 1306A, each comprise vehicle
presence
and direct axle detectors which are similar to those described previously, and
are spaced
150 meters apart. Sensor array 1307 is positioned I50 meters beyond the sensor
array
1305 and comprises a vehicle presence detector and a direct axle sensor.
Sensor arrays
1711 (namely, 1711J, 1711K), 1305, 1305A, 1306, 1306A and 1307, 1307A, are
connected to a roadside controller 1408 similar to that of the other
embodiments,
including a processor and a modem 1409 (FIG 14). As shown in Figure 14, the
roadside
controller is connected to traffic signal controller 1401 which controls the
sequence of
the traffic signals 1402 and also a camera 1401 which is located adjacent the
traffic
signals.
As a vehicle traverses the zones of the sensor arrays, namely station #1
sensors,
station ~l2 sensors and station #I3 sensors, the processor determines the
truck type, and
the speed, using the signals from the sensor arrays 1711(namely, 1711J,
1711K), 1105,
1306. If the vehicle is a truck, using the preprogrammed site-specific data,
including site
characteristics, e. g. , length and severity of the downgrade, the processor
computes a
maximum speed for that particular class of truck. From the signals from the
sensor array
CA 02238127 1998-OS-15
42
1306, 1306A, the processor determines whether or not the truck is exceeding
the
calculated maximum speed and whether the speed of the truck has increased
significantly,
or decreased, between the sensor arrays 1305, 1305A, 1306, 1306A. If the speed
of the
truck as it traaerses the sensor 1306, 1306A, is greater than the calculated
maximum
value, indicating that the truck cannot stop safely at the intersection, the
processor
transmits a pre-empt signal to the traffic signal controller 1401 which
ensures that the
traffic signals are in favour of the truck when it arrives at the
intersection.
The specific sequence of operations is illustrated in FIGS. 15A and 15B. On
receipt of a signal from sensor arrays 1711D, 1305, the processor determines,
in steps
15.1 and 15.2, whether or not a truck has been accurately detected. If not,
step 15.3
records an error. If the truck has been accurately detected, the processor
processes the
signals from electro-acoustic sensors 1711 (namely 1711J, 1711K), and signals
from
sensor arrays 1305, 1305A, 1306, 1306A, in step 15.4, to compute vehicle
speed,
bumper to bumper length, axle spacings and number of axles, measures or
assumes the
weight, and adds the time and date to the data before recording it. If the
controller has
problems processing any of the signals from the sensors in the sensor array, a
warning
or error is added to the vehicle information to indicate that the calculated
values may be
in error. From the vehicle information, the processor uses stored data or
"look-up"
tables to determine vehicle type, based upon the length of the vehicle, the
number of
axles and the distance between each axle. From this classification, the
processor
determines, in decision step 15.5 whether or not the vehicle is a truck. If it
is not, the
processor takes no further action with the data, as indicated in step 15.6. If
the vehicle
data indicates that it is a truck, however, the processor computes, in step
15.7, a
maximum safe speed for that truck based upon its configuration.
Upon receipt of a signal from second sensor 1306, 1306A, in step 15.8, the
processor again determines whether or not the truck has been accurately
detected (step
15.9). If it has not, a truck error is recorded in step 15.10. If the
controller has
problems processing any of the signals from the sensors in the sensor array, a
warning
or error is added to the truck information to indicate that the calculated
values may be
in error. If the truck has been accurately detected at sensor 96, the
processor processes
CA 02238127 1998-OS-15
43
the signals from sensor 1306, 1306A, in step 15.11 to determine the truck
speed, bumper
to bumper length, axle spacings and number of axles, and measures or assumes
the
weight. In step 15.12, it compares the actual truck speed measured at sensor
1305,
1305A, with the actual truck speed measured at sensor 1306, 1306A. If the
speed at
sensor # 1 is greater than the speed at sensor # 2, the speed at sensor # 1 is
used, at
decision step 15.23. If the speed at sensor # 1 is not greater than the speed
at sensor #
2, the speed at sensor # 2 is used, at decision step 15.22. The controller, by
the use of
the selected speed, obtains, from tables, a maximum stopping threshold for
that truck
classification. The stopping threshold will be based on standardized tables
for each truck
configuration.
When a signal is received from sensor array 96, the processor again checks
that
the truck has been detected accurately (steps 15.14, 15.15) and records an
error if it has
not. If it has, in step 15.16 the processor processes the signals from sensor
1711 to
produce a record of to the truck speed, bumper to bumper length, axle spacings
and
number of axles, and measures or assumes the weight, and adds a time and date
stamp
as before. If the processor has problems processing any of the signals from
the sensors,
a warning or error is added to the truck information to indicate that the
calculated values
may be in error. Based on the stopping threshold information determined in
step 12.13,
and the truck speed measured at sensor 1307, the processor will determine in
step 12.17
whether or not the truck will be able to stop before the intersection if the
traffic signal
requires it. If decision step 15.17 indicates that it will be able to stop,
the processor
takes no further action as in step 15.18. However, if decision step 15.7
indicates that
it will not be able to stop, the processor sends a signal to the traffic
signal controller 100
as indicated in step 15.19, causing it to pre-empt the traffic signal to keep
the traffic
flowing continuously in the direction the truck is travelling. The pre-emption
signal will
override the traffic signal sequence either to change the traffic signal to
favour the
passage of the vehicle or, if it is already in its favour, to ensure that the
traffic signal
does not change for a suitable interval. The duration of the traffic signal
pre-emption
is based upon site specific geometrics and varies from site to site. The
central controller
can also be programmed to pre-empt the traffic signal as a precautionary
measure when
CA 02238127 1998-OS-15
44
a warning or error occurs at any or all of the sensor arrays 1305, 1305A,
1306, 1306A,
1307 and 1307A.
As before, as an option to the main detection sensors, on-scale detectors may
be
incorporated into each lane to ensure that the vehicles passing the sensor
arrays are fully
within the active zone of the system, and are not straddling a lane. The on-
scale
detectors effectively eliminate the possibility that a truck will receive a
message for a
speed that is higher than is safe for that particular truck.
It will be appreciated that there is potential for abuse, i.e. drivers
deliberately
causing the system to pre-empt the traffic signals. Accordingly, whenever the
traffic
signal controller 1401 receives a pre-emption signal, it operates the roadside
camera
1403, as indicated by step 15.20, to capture an image of the vehicle which
caused the
pre-emption signal. The video record will provide a means of identifying
vehicles for
safety and regulatory purposes.
As in the case of the other embodiments, all vehicle data collected from
electro-
acoustic sensors 1711 (namely, 1711J, 1711K), 1305, 1305A, 1306, 1306A 1307
and
1307A can be transmitted, via modem, to a central computer for analysis at
step 15.21.
In any of the embodiments of the invention, the controller may be reprogrammed
with fresh data and table information, conveniently by means of, for example,
a laptop
computer. Moreover, instead of the data being transmitted via modem to the
central
computer, the data could be stored in the memory of the controller and
retrieved
periodically by, for example, a laptop computer. A remote terminal can be used
to
provide full remote control over the operation of the system, including
controls, e.g.,
disabling the system or overriding signal pre-emption where there is a false
alarm.
An advantage of traffic monitoring systems embodying the present invention is
that they perform real-time computations using information specific to a
particular vehicle
without necessarily knowing the weight of the vehicle and information specific
to a
particular potential hazard to determine what message, if any, to display to
the driver of
the vehicle or, in the case of the traffic signal pre-emption system, whether
or not to pre
empt the regular traffic signal. Hence, the system recommendations are
tailored to the
site and the specific vehicle. Consequently, there is less likelihood of
erroneous or
CA 02238127 1998-OS-15
untimely messages being displayed and hence increased likelihood that drivers
will heed
the messages and/or not abuse the system.
In each embodiment of the invention, the controller may also have an auto-
calibration feature. If the system fails for any reason, an alert signal is
transmitted to
5 the host computer via modem, informing the system operators of a system
malfunction.
The set of electro-acoustic sensors 1711,(namely 1711A, 1711B, 1711C, 1711D,
1711E, 1711F, 17116, 1711H, 1711I, 1711) and 1711K) are based on an
improvement
on a system which is used to monitor highway traffic, and will be described
more fully
hereinafter with reference to FIGS 17 to 21.
10 (v) DESCRIPTION OF ELECTRO-ACOUSTIC SENSOR MOUNT
As seen in Fig. 16, the electro-acoustic sensors 1711, designated 1601A and
1601B, are mounted on a mast arm 1602. The mast arm 1602 is supported on a
sensor
mounting pole 1603, which includes a pole-mounted cabinet 1604. The pole-
mounted
cabinet houses the controller electronics of the above-road electro-acoustic
sensors,
15 known by the trade-mark SmartSonicT"'. The pole mounted cabinet provides
protection
in a harsh outdoor environment, including protection from vandalism, rain,
sleet, snow,
dripping water, corrosion, hosedown, splashing water, and oil or coolant
seepage. The
sensor mounting pole 1604 is optionally provided with a breakaway base 1605.
Beneath
the roadway or the shoulder of the roadway is an electrical junction box 1606.
20 Typically the mast arm is 10 feet long, and the sensor mounting pole is 20
feet
high. The sensors are mounted on poles and are aimed at specific areas on the
roadway
through which the traffic will pass. Since two lanes are to be equipped at
this site,
sensors are installed on both shoulders. For each lane, two detection zones
are used.
The above-road electro-acoustic sensors provide data which is processed by the
controller
25 electronics to determine a vehicle speed.
(vi) ELECTRO-ACOUSTIC SENSORS
FIGS 17 to 21 will now be described with respect to the electro-acoustic
sensors
1711, (namely 1711A, 1711B, 1711C, 1711D, 1711E, 1711F, 17116, 1711H, 1711I,
1711) and 1711K). Each motor vehicle using a highway radiates acoustic energy
from
30 the power plant (e. g. , the engine block, pumps, fans, belts, etc.) and
from its motion
CA 02238127 1998-OS-15
46
along the roadway (e.g., tire noise due to friction, wind flow noise, etc.).
While the
energy fills the frequency band from DC up to approximately l6KHz, there is a
reliable
presence of energy from 3KHz to 8KHz. Thus an analysis of such energy enables
the
classification of the vehicle as a truck or as not a truck.
Fig. 17 depicts an illustrative embodiment of an electro-acoustic sensor array
constituting an essential element of the systems of the present invention,
which includes
the monitoring of a predetermined area of roadway, called a "predetermined
detection
zone", for the presence of a motor vehicle and for the classification of such
vehicle as
a truck within that area. The salient items in Fig. 17 are roadway 1701,
automobile
1703, truck 1705, detection zone 1707, microphone array 1711, microphone
support
1709, detection circuit 1715 and interface circuit 1719 in a roadside cabinet
(not shown),
electrical bus 1713, electrical bus 1717 and lead 1721, which conducts a loop
relay signal
to a command centre.
Each omni-directional microphone in microphone array 1711 receives an acoustic
signal which comprises the sound radiated, inter alia, from automobile 1703,
truck 1705
and ambient noise. Each microphone in microphone array 1711 then transforms
its
respective acoustic signal into an analog electric signal and outputs the
analog electric
signal on a distinct lead on electrical bus 1713 in ordinary fashion. The
respective
analog electric signals are then fed into detection circuit 1715.
To determine the presence or passage of a motor vehicle in predetermined
detection zone 1707, the respective signals from microphone array 1711 are
processed
in ordinary fashion to provide the sensory spatial discrimination needed to
isolate sounds
emanating from within predetermined detection zone 1707. The ability to
control the
spatial directivity of microphone array 111 is called "beam-forming". It will
be clear to
those skilled in the art that electronically-controlled steerable beams can be
used to form
multiple detection zones. The analysis of the sounds which emanate from the
predetermined detection zone 1707 broadly classifies a vehicle according to
its length,
the number of axles and the spacing of the axles, i.e., as a truck or not as a
truck.
As shown in Fig. 18, microphone array 1711 preferably comprises a plurality of
acoustic sensors 1801, 1803, 1805, 1807, 1809, 1811, 1813, 1815 and 1817, (e.
g.,
CA 02238127 1998-OS-15
47
omni-directional microphones), arranged in a geometrical arrangement known as
a Mill's
Cross. For information regarding Mill's Cross arrays, the interested reader is
directed
to Microwave Scanning Antenna, R.C. Hensen, Ed., Academic Press (1964), and
Principals of Underwater Sound (3rd. Ed). R. J. Urick (1983). While microphone
array
1711 could comprise only one microphone, the benefits of multiple microphones
(to
provide signal gain and directivity, whether in a fully or sparsely populated
array or
vector), will be clear to those skilled in the art. It will also be clear to
those skilled in
the art how to baffle microphone array 1711 mechanically so as to attenuate
sounds
coming from other than predetermined detection zone 1707 and to protect
microphone
array 1711 from the environment (e.g., rain, snow, wind, UV).
Microphone array 1711 is advantageously rigidly mounted on support 1709 so
that
the predetermined relative spatial positionings of the individual microphones
are
maintained. The microphone array 1711 may include a set of microphone arrays
which
are mounted on a mast arm which is supported on a pole, and another set of
microphone
arrays which are mounted the pole itself. Alternatively, the sets of
microphone arrays
may be mounted on a highway overpass. The height above the road may be 20 to
35
feet to aim at a point of up to 25 feet. The detection zone typically may
cover an area
of 4 to 8 feet by 6 to 12 feet. A typical deployment geometry is shown in Fig.
17. In
that particular geometry, the horizontal distance of the sensor from the
nearest lane with
traffic is assumed to be less than 15 feet. The vertical height above the road
is
advantageously between 20 and 35 feet, depending on performance requirements
and
available mounting facilities. It will be clear to those skilled in the art
that the
deployment geometry is flexible and can be modified for specific objectives.
Furthermore, it will also be clear to those skilled in the art how to position
and orient
microphone array 1711 so that it is well suited to receive sounds from
predetermined
detection zone 1707.
(vii) DETECTION CIRCUIT
Referring to now to Fig. 19, detection circuit 1715 (See Fig. 17)
advantageously
comprises bus 1713, (See Fig. 17) bus 1903, vertical summer 1905, analog-to-
digital
converter 1913, finite-impulse-response (FIR) filter 1917, bus 1903,
horizontal summer
CA 02238127 1998-OS-15
48
1907, analog-to-digital converter 1915, finite-impulse-response (FIR) filter
1919,
multiplier 1921 and comparator 1925. The electric signals from microphone
1801,
microphone 1803, microphone 1805, microphone 1807 and microphone 1809 (as
shown
in Fig. 18) are fed, via bus 1901, into vertical summer 1905 which adds them
in well-
s known fashion and feeds the sum into analog-to-digital converter 1913. While
in the
illustrative embodiment, vertical summer 1905 performs an unweighed addition
of the
respective signals, it will be clear to those skilled in the art that vertical
summer 1905
can alternatively perform a weighted addition of the respective signals so as
to shape and
steer the formed beam (ie., to change the position of predetermined detection
zone 1707).
It will also be clear to those skilled in the art that illustrative
embodiments of an electro-
acoustic sensor array providing systems constituting essential elements of the
present
invention can comprise two or more detection circuits, so that one microphone
array can
gather the data for two or more detection zones, in each lane or in different
lanes.
Analog-to-digital converter 1913 receives the output of vertical summer 1905
and
samples it at 32,000 samples per second in well-known fashion. The output of
analog-to-
digital converter 1913 is fed into finite-impulse response filter 1917.
Finite-impulse response filter 1917 is preferably a bandpass filter with a
lower
passband edge of 4KHz, an upper passband edge of 6KHz and a stopband rejection
level
of 60dB below the passband (i.e., stopband levels providing 60dB of
rejection). It will
be clear to those skilled in the art how to make and use finite-impulse-
response filter 317.
The electric signals from microphone 1811, microphone 1813, microphone 1805,
microphone 1815 and microphone 1817 (as shown in Fig. 18) are fed, via bus
1903, into
horizontal summer 1907 which adds them in well-known fashion and feeds the sum
into
analog-to-digital converter 1915. While in the illustrative embodiments,
horizontal
summer 1907 performs an unweighed addition of the respective signals, it will
be clear
to those skilled in the art that horizontal summer 1907 can alternatively
perform a
weighted addition of the respective signals so as to shape and steer the
formed beam
(i.e., to change the position of predetermined detection zone 1707).
CA 02238127 1998-OS-15
49
Analog-to-digital converter 1915 receives the output of horizontal summer
1905,
and samples it at 32,000 samples per second in well-known fashion. The output
of
analog-to-digital converter 1913 is fed into finite-impulse response filter
1919.
Finite-impulse response filter 1919 is preferably a bandpass filter with a
lower
passband edge of 4KHz, an upper passband edge of 6KHz and a stopband rejection
level
of 60dB below the passband (i.e., stopband levels providing 60dB of
rejection). It will
be clear to those skilled in the art how to make and use finite-impulse-
response filter
1919.
Multiplier 1921 receives, as input, the output of finite-impulse-response
filter 317
and finite-response-filter 1919 and performs a sample-by-sample multiplication
of the
respective inputs and then performs a coherent averaging of the respective
products. The
output of multiplier 1921 is fed into comparator 1925. It will be clear to
those skilled
in the art how to make and use multiplier 1921.
Comparator 1925 advantageously, on a sample-by-sample basis, compares the
magnitude of each sample to a predetermined threshold and creates a binary
signal which
indicates whether a motor vehicle is within predetermined detection zone 1707.
While
the predetermined threshold can be a constant, it will be clear to those
skilled in the art
that the predetermined threshold can be adaptable to various weather
conditions and/or
other environmental conditions which can change over time. The output of
comparator
1925 is fed into interface circuitry 1719.
Interface circuitry 1719 receives the output of detection circuitry 1715 and
preferably creates an output signal such that the output signal is asserted
when a motor
vehicle is within predetermined detection zone 1707 and such that the output
signal is
retracted when there is not motor vehicle within the predetermined detection
zone 107.
Interface circuitry 1719 also makes any electrical conversions necessary to
interface to
the circuitry at the command centre of the highway department. Interface
circuitry 119
can also perform statistical analysis on the output of detection circuitry
1715 so as to
output a signal which has other characteristics than those described above.
CA 02238127 1998-OS-15
(viii) MAXIMALLY-DIGITAL IMPLEMENTATION
Figure 20 illustrates a practical, maximally-digital, implementation. The
microphone array 2000 comprises two vertical elements V, and V2, and two
horizontal
elements H, and H2. As shown, each element has three microphones, which was
found
5 practically sufficient. Each of the four elements V~, V2, H, and H2 feeds a
respective
analog filter 2001 to 2004 to attenuate unwanted noise outside the maximal
frequency
band of interest, which is normally between 4 and 9 kHz. The filters 2001 to
2004 are
each followed by a respective selectable gain pre-amplifier 2005 to 2008, the
gain of
which is selectable in 3-Db steps ranging from OdB to lSdB (hereinafter to be
described
10 more fully later). Four respective analog-to-digital converters 2009 to
2012 follow the
pre-amplifiers 2005 to 2008. Respective digital finite impulse response (FIR)
filters 2013
to 2016 follow the A/D convertors 2009 to 2012. The FIR filters 2013 to 2016
determine the actual frequency band of operation, which is selected from the
following
four bands:
15 Band 1 : 4-6 Khz;
Band 2 : 5-7 Khz;
Band 3 : 6-8 Khz; and
Band 4 : 7-9 Khz.
20 One value for the gain of all of the pre-amplifiers 2005 to 2008 will
normally be selected
for the four above bands as follows:
Band 1 Band 2 Band 3 Band 4
9dB lldB l3dB lSdB
6dB 8dB lOdB l2dB
25 3dB SdB 7dB 9dB
OdB 2dB 4dB 6dB
The selection of the frequency band would normally depend on the general
nature
of the expected vehicle traffic at the particular location of the sensor. The
selected gain
30 would depend, in addition, on the distance of the sensor from the road
surface. The
outputs of the FIR filters 2013 and 2014 (the paths of V, and VZ) are summed
in digital
summer 2017, while the outputs of FIR filters 2015 and 2016 (the paths of H,
and HZ)
are summed in digital summers 2017 and 2018. The respective digital summers
2017
CA 02238127 1998-OS-15
51
and 2018 are followed by digital limiters 2019 and 2020, respectively, and the
outputs
of the latter are input to correlator 2021, the output of which is fed to a
parallel-to-serial
convertor 2022, the serial output of which would normally be fed to a TDMA
multiplexer (TMDA-MUX) 2023 to be time-division multiplexed with other
(conveniently
four) processed microphone array signals originating from overhead locations
near the
array 2000. The multiplexed output of the TMDA-MUX 2023 is then normally
relayed
by cable 2024 to roadside microprocessor-based controller 2025, where it is
demultiplexed in DEMUX 2026 into the original number of serial outputs
representing
the serial outputs of correlators, e.g., 2021. After demultiplexing in DEMUX
2026, the
cross-correlated digital output from the correlator 2021 is integrated in
integrator 2027
(which could be a software routine in the microprocessor/controller 2025),
and,
depending on the correlated/integrated signal level, which is compared to a
threshold in
vehicle detector 2028, a "vehicle present" signal is issued for the duration
above
threshold. This information is processed by a flow parameter calculation
routine 2029
of the controller 2025, the output of which is an RS232 standard in addition
to hard-
wired vehicle presence circuits or relays (not shown).
(ix) OPERATION OF CONTROLLER
The operation of the controller 2025, whereby the demultiplexed signal from
DEMUX 2026 is processed, will be better explained by reference to the flow-
chart
shown in Figure 21. The signal is adjusted in gain/offset 2100 depending on
user-
specific parameters 2101 and then sampled at 2102 and integrated at 2103. The
signal
sampling 2103 continues until enough samples at 2104 have been collected, upon
which
the integrator 2103 is reset at 2105 and the mode is determined at 2106. If
the mode is
initially to indicate vehicle presence, and a vehicle is detected at 2107,
which by sound
analysis as hereinbefore described, classifies the vehicle as a truck, the
decision is
immediately outputted at 2107. If the mode 2106 is "free flow", then long term
speed
average is calculated at 2109 from which variable thresholds are progressively
calculated
at 2110. That is, the more vehicles there are, the more accurate will the
average
progressively become. This variable threshold is used to continue to determine
vehicle
presence at 2111, and to calculate flow parameters 2112. For example, from the
average
CA 02238127 1998-OS-15
52
speed and the time the vehicle is in the detection zone, the length of the
vehicle is
determined, and the truck classification is confirmed. This progressively
yields a better
determination of the speed of the particular vehicle, given the length of the
detection
zone. The latter, of course, depends on the frequency band and the distance of
the
microphone array 2000 from the road surface. On average, in many applications,
the
length of the detection zone 1707 would be approximately six feet. The flow
parameters
2112 are stored in memory 2113 and outputted at 2114 over the RS232 serial
link to
(other) central traffic management systems (not shown), and where desired
activate other
interface circuits. As may be seen, the "free flow" processing is iterative in
nature,
while the binary vehicle presence decision 2106 is determined by a user
selected fixed
threshold 2108.
